1. Field of the Invention
The present invention relates in general to switching regulator systems, and more particularly to a scalable input current switching regulator system with low quiescent current useful for weak power sources.
2. Description of the Related Art
The load profile of microcontroller-based systems is often characterized by long periods of very low load currents while the microcontroller is in a quiescent, idle state, punctuated by short periods of high load currents when the microcontroller wakes up and controls some activity, such as a brief radio transmission or other higher power operation. Small batteries, solar cells, and other “weak” power sources may be capable of supplying the average load to these systems, but may not be capable of supplying the peak current needed during the periods of high load currents.
Furthermore, some loads in the system may require a higher voltage or a lower voltage than that provided by the input source. A conventional switching regulator may be employed to extract power from the source and provide a useable, regulated voltage, but excessive current may be drawn from the input source during the periods of high load currents. When excessive current is drawn from a battery, a voltage drop through the series impedance of the battery results in wasted power. Small batteries typically maintain the longest life when current is drawn at low levels. Repetitive periods of excessive current generally shortens battery life.
A large output capacitor may be placed at the output of the regulator to buffer the peak loads. A typical switching regulator, however, attempts to recharge the capacitor at an uncontrolled rate, which is usually a high rate, again drawing excessive current from the source. A current limit at the switching output of the regulator does not solve this problem, since the actual current drawn from the source varies as the source voltage varies and the output voltage changes with the charging output capacitor.
Some peripherals in the system, such as a radio or the like, may operate intermittently and require a regulated voltage only during operation. When not operating, however, the peripheral may still draw a small, yet finite unwanted leakage current that may adversely impact battery life. If the regulated voltage is generated by a switching regulator, the switching regulator may be switched off when the peripheral is off in order to remove power from the peripheral to prevent the unwanted leakage current draw. In conventional systems, prior to the peripheral being turning on, the microcontroller had to estimate the time required for the switching regulator to bring up the regulated voltage before allowing the peripheral to turn back on. This activation time was often significant, and variable, constraining the system to be configured to handle the latency and causing significant challenges for providing fast reacting peripherals.